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        从浏览器输入分数[ 0~100之间 ]，使用switch判断，不同分数所属的级别：
            90 <= score <= 100   A级  十位数是9 10
            80 <= score < 90     B级
            70 <= score < 80     C级
            60 <= score < 70     D级
            0 <= score < 60      E级

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